I used to replace the pads on my FIAT with a screwdriver, pliers, a hammer and a C clamp.
1-Pull cotter pins on shims with pliers 2-Drift out the shims by tapping on them with screwdriver/hammer 3-With pad out use C-clamp to push caliper piston back far enough so new pad will fit. 4-Reverse processI now have a '93 Impreza LS with front and rear discs (14" wheels). Is the above process going to work or are there some tricks to the Subaru's?